496 



MESOZOIC ERA— AGE OF REPTILES. 



vailed, the deposits are undoubtedly Cretaceous. When lake-conditions 

 are fairly established, they are undoubtedly Tertiary ; the intermediate 

 brackish-water deposits are the Laramie. But, as the change was 

 gradual and the sedimentation continuous, of course the strata were 



in places conformable 

 throughout. 



In regard to the 

 Life-system the expla- 

 nation is similar. The 

 abolition of the interi- 

 or Cretaceous sea and 

 the unification of the 

 continent was a great 

 event, and produced 

 very great change in 

 physical conditions. 

 There was, therefore, a 

 corresponding change 

 in the Life-system. 

 But this was also grad- 

 ual. The Cretaceous 

 Dinosaurs still lingered, 

 ready to disappear ; but 

 as new land appeared 



s£<^\ 



m?m^ 



Fig. 830. Fig. 831. 



Figs. 829-831.— 829. Aralia digitata. 830. Leguminositis arachioides. 831. Populus cuneata. 



